Bartonella quintana (BQ) is a bacterial pathogen that persists for months in the human bloodstream, and causes relapsing fever, heart valve infection, and vascular proliferative lesions. BQ infection produces debilitating or fatal illness in immunocompromised individuals. It can also cause serious infections in people with a normal immune system. Little is known about the mechanisms by which this recently identified pathogen is able to Infect humans and cause disease. One important aspect of BQ pathogenesis is attachment to and infection of red blood cells (RBC), which enables BQ to both circulate throughout the body and escape detection by the host immune system. We sought to understand mechanisms by which BQ adheres to host cells and evades the host immune system, and identified a family of four variably-expressed outer membrane protein (Vomp) adhesins that are involved in the binding of BQ to host cells, including RBC. The Vomp are required for infection in vivo, and share homology with the trimeric autotransporter adhesin (TAA) protein family, which includes Yersinia YadA and Neisseria NadA. The TAA are transported across the outer membrane via the type Vc secretion system, and form trimers on the bacterial surface. As outlined in this proposal, I will investigate the functional structure of the Vomp, and determine the host cells to which these Vomp adhesins bind. The specific aims of this proposal are: 1) characterization of the Vomp functional structure in the bacterial outer membrane;2) identification of the role of Vomp in binding of BQ to RBC;and 3) analysis of the role of individual Vomp in binding to the extracellular matrix (ECM). Functional testing of Vomp mutants will identify the domains critical for Vomp function. The surface architecture (heterotrimerization and/or homotrimerization) of the Vomp will be elucidated using immunoprecipitations followed by mass spectrometry. A flow cytometry-based assay and confocal microscopy will examine BQ or individual Vomp binding to RBC. Interaction of the Vomp with ECM components will be tested using an ELISA-based assay to examine the role of Vomp in targeting BQ to multiple host tissues. PUBLIC HEALTH RELEVANCE: BQ infection causes devastating illness in immunocompromised patients, and serious infections in immunocompetent people. This proposal will study the Vomp, a family of virulence proteins expressed on the bacterial surface that are necessary for successful BQ infection. Understanding how this emerging pathogen causes disease in humans will lead to better strategies to combat BQ infection.